Androgenic Modulation of Cyclic Adenosine Monophosphate (cAMP)-Dependent Meiotic Arrest

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Abstract
A previous finding that testosterone synergizes with dibutyryl cAMP (dbcAMP) to arrest the meiosis of a very high proportion of cumulus-enclosed (intact) pig oocytes in vitro was investigated further, suggesting that estradiol may have mediated in this synergism. The effects of androgens [testosterone (T), 0.5 .mu.M; dihydrotestosterone (DHT), 0.5 .mu.M], estradiol (E2), 0.5 .mu.M, gonadotropins [NIH [National Institutes of Health] FSH, 0.1-10 .mu.g/ml; highly purified (hp) FSH, 0.1 .mu.g/ml; luteinizing hormone (hpLH), 30 ng/ml], and dbcAMP, 1 mM, on the maturation of liberated intact or cumulus-free (denuded) oocytes were investigated. In 1 series of experiments, intact oocytes were cultured in medium containing T with NIH-FSH (10 .mu.g/ml) with or without the steroid biosynthesis inhibitor, cyanoketone (0.7 .times. 10-7 M). After culture for 6-48 h, oocytes were air-dried for cytogenetic analysis, the meiotic stage was scored and in some cases spent media were analyzed by radioimmunoassay for E2 and progesterone (P4) content. After 24 h of culture, FSH and dbcAMP similarly and significantly arrested meiosis of intact oocytes (45 and 43% matured, respectively), but the arresting actions of these compounds were modulated quite differently by androgen; that of dbcAMP was significantly enhanced by T, while that of FSH was significantly depressed by T and DHT. Nevertheless, FSH with T transiently maintained meiotic arrest since a very high proportion of oocytes remained at the germinal vesicle (GV) stage after 12 h of culture, compared with controls (95 and 45% at GV stage, respectively). No difference was detected between impure NIH-FSH and hpFSH relative to the meiotic progression of intact oocytes and hpLH with T did not duplicate the arresting actions of either FSH preparation. This transient arresting action of FSH with T was mediated by the adherent cumulus cells since the maturation of denuded oocytes was not affected by FSH, T or FSH with T. While substitution of T with E2 did not duplicate this cumulus cell-mediated androgenic effect, the modulations exerted by DHT on either dbcAMP- or FSH-induced meiotic arrest were not as marked as those exerted by T. Analysis of E2 and P4 in the spent media of intact oocytes cultured for 6 or 12 h in the presence of FSH with T revealed positive correlations between the proportion of immature oocytes and the E2:P4 ratio in the media. Compared with controls, meiotic arrest was maintained for up to 24 h in medium containing cyanoketone with T and FSH, and positive correlations were established between the proportion of GV oocytes and the E2:P4 ratio in the spent media. Androgens apparently have the capacity to modulate cAMP-dependent meiotic arrest in vitro and the expression of this modulation may be regulated by the aromatase system and/or the E2:P4 status of the adherent cumulus cells. These findings are considered in light of the 2 currently popular hypotheses regarding the mechanisms which control meiotic maturation.